linux-kernel - Re: [PATCH v1] drivers/perf: apple_m1: fix affinity table for event 0x96 and 0x9b

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Date: Tue, 2 Jul 2024 18:22:21 +0800
From: Yangyu Chen <cyy@...self.name>
To: Marc Zyngier <maz@...nel.org>
Cc: Will Deacon <will@...nel.org>,
 linux-arm-kernel@...ts.infradead.org,
 Mark Rutland <mark.rutland@....com>,
 Janne Grunau <j@...nau.net>,
 Hector Martin <marcan@...can.st>,
 Asahi Lina <lina@...hilina.net>,
 asahi@...ts.linux.dev,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] drivers/perf: apple_m1: fix affinity table for event
 0x96 and 0x9b

> Yangyu, can you please clarify how you came to the conclusion that
> these events didn't count anywhere other than counter 7?
> 

IIRC, I came across some web page that says events 0x96 and 0x9b
can only be installed on counter 7 to count Apple AMX, but I can't
find the page now. Since AMX is not usable in Linux, I don't know
if this will affect some other instructions that are usable in
Linux.

There are some other reasons, but I can't say in public.

Even though I can't find the actual usage, I think using count 7
only for these 2 events is safer. If this reason is insufficient,
we can ignore this patch until we find other evidence that this
affinity affects some instructions usable in Linux.

Thanks,
Yangyu Chen